Now that the North Coast is finally drying out from an unusually wet winter, concern is growing over the potential rapid spread of sudden oak disease, renewing calls for the public’s help tracking the deadly forest pathogen.

“Now is when we might expect the pathogen to take off a bit,” said Kerry Wininger, a UC Cooperative Extension staffer in Santa Rosa.

Wininger is a local organizer of annual sudden oak death surveys known as the SOD Blitz. This year’s survey occurs from April 25 to 28 across Sonoma and Mendocino counties. Organizers are hoping for a good turnout of volunteers, who will become educated spotters and collectors to help scientists slow the disease’s spread.

A relatively dry winter in 2017-18, coupled with the attention paid to devastating wildfires, appear to have dampened public concern over sudden oak death. But experts say conditions are ripe now for a resurgence of the disease. In addition, there’s heightened worry about a new, more virulent strain of the pathogen gaining a hold on the North Coast and causing more devastation.

Wininger said one of the highlights of this year’s surveys is the unveiling of a new test for the European strain in time to possibly thwart its spread. The new strain has been detected in Oregon.

“We want to nip it in the bud, if it’s here,” Wininger said.

Phytophtora ramorum, the pathogen that causes SOD, most often is spread by water droplets blowing from the leaves of infected bay laurel trees. There is no cure, only preventative measures or destroying oak and tanoak trees that succumb to the pathogen.

A dry winter curtailed the presence of a deadly forest pathogen this year in Sonoma County and 13 other Northern and Central California counties, but experts still expect the oak-killing disease to spread and warned landowners to be vigilant.

Since the mid-1990s, sudden oak death has killed up to 50 million trees from Big Sur to southwest Oregon and is entrenched in the woodlands, spreading rapidly after wet winters and slower during dry years.

Cobb said Monday he’s about to publish his estimate of tree mortality, 90 percent of which are tanoaks and most of the rest coast live oaks. Another 100 million trees may be infected by the insidious pathogen that typically takes one or two years to produce symptoms in the infected trees, he said.

The pathogen can be spread by human footprints and nursery plants, but in nature it rides on water droplets blown from the leaves of bay laurel trees, a host species that abounds among the oak and tanoak trees susceptible to the disease.

Guy Kovner, THE PRESS DEMOCRAT
Rejuvenated by two straight wet winters, the insidious pathogen that has killed more than 3 million trees in Central and Northern California in the past two decades reached a record level of infection this year, including major gains in Sonoma County.
The spread of sudden oak death could further transform North Coast forests already ravaged by drought and altered by climate change, increasing their vulnerability to catastrophic fire.
The lethal pathogen is spread largely by wind-blown water droplets and resides in bay laurel trees without harm but can infect and ultimately kill four species of oaks, the fire-resistant native hardwoods that cover coastal ranges and inland valleys and hillsides. Their displacement, in favor of bay trees and conifers, could raise fire risks across the region.
“If you’ve had sudden oak death for 20 years, my guess is the forests will be worse off,” said Matteo Garbelotto, director of the forest pathology and mycology laboratory at UC Berkeley, which oversees the annual sudden oak death survey.
Results of the latest survey showed a 10-fold increase over 2015 — from 3.8 percent to 37 percent this year — in the sudden oak death infection rate in an area that includes Healdsburg, Santa Rosa, Sonoma and Petaluma. That level of infection, which stunned researchers, was matched or exceeded in only three other parts of the 17-county survey area.
The infection rate doubled north of Healdsburg and increased slightly less west of Highway 101, where the infection is already rampant in the hills west of Sebastopol.
Read more at: Sudden oak death rampant in Sonoma County after two wet winters, raising longterm fire risks